I.  DEFINITION

Cough ( Latin : tussis ) is a sudden, forceful noisy expulsion of air from the lungs. The three stages of coughing are preliminary inspiration, glottal closure and contraction of respiratory muscles, followed by sudden glottal opening to produce the outward blast of air.

II.  PATHOPHYSIOLOGY

The sensory nerve endings for the cough reflex are branches of the vagus in the larynx, trachea, and bronchi; but cough also be induced by stimulation in the external acoustic meatus that is supplied by the auricular nerve ( Arnold nerve), a branch of vagus. Stimuli to coughing include exudates in the pharynx or bronchial tree, irritation of foreign bodies, and inflammation. Coughing may be voluntary or involuntary, single or paroxysmal. A cough in which sputum is raised is productive. A brassy cough is unproductive and has a strident quality. It occurs in any condition that narrows the trachea or glottal space, most commonly laryngitis or epiglottitis, but also laryngeal paralysis, neoplasm of vocal cord, or aortic aneurysm.

III. PATHOGENESIS

Frequent or severe coughing usually indicates the presence of a disease . Many viruses and bacteria benefit by causing their host to cough, which helps to spread the disease to new hosts. Coughing is classified as acute (of sudden onset) if it is present less than three weeks,subacute if it is present between three and eight weeks, and chronic when lasting longer than eight weeks. A cough can be dry or productive, depending on whether sputum is coughed up. Most of the times, coughing is acute and caused by a respiratory tract infection . Coughing can be triggered by food entering the windpipe rather than the esophagus due to a failure of the epiglottis in patients who havedifficulties swallowing . Smoking and air pollution are common causes of coughing. [1] Provided the patient is a non-smoker and has a normal chest X-ray , the three most common causes of chronic cough are asthma , gastroesophageal reflux disease and post-nasal drip . Other causes of chronic cough include chronic bronchitis , heart failure and medications such as ACE inhibitors .

Since cough is a natural protective reflex, suppressing the cough reflex might have deleterious effects, especially if the cough is productive.[2] Nonetheless, coughing might be severe enough (in terms of psychological, physical and social distress) to warrant treatment. This should be targeted towards the cause as much as possible, for example by smoking cessation and discontinuing ACE inhibitors. Some patients may only be worried about serious illnesses, and reassurance may suffice. Cough suppressants (or antitussives) such as codeineor dextromethorphan are frequently prescribed although scientific evidence supporting their use is often of poor quality. Other treatment options may target

The common causes of chronic dry coughing include post-nasal drip , gastroesophageal reflux disease , asthma , post viral cough and ACE inhibitors . When coughing is the only complaint of a person who meets the criteria for asthma ( bronchial hyperresponsiveness and reversibility), this is termed cough-variant asthma . Two related conditions are atopic cough and eosinophilic bronchitis . Atopic cough occurs in individuals with a family history of atopy , abundant eosinophils in the sputum, but with normal airway function and responsiveness. Eosinophilic bronchitis is also characterized by eosinophilia in the sputum, without airway hyperresponsiveness or an atopic background. This condition responds to treatment with corticosteroids .

Individuals who smoke often have a smoker’s cough , a loud, hacking cough which often results in the expiration of phlegm . Coughing has also been linked to air pollution .

A foreign body can sometimes be suspected, for example if the cough started suddenly when the patient was eating. Rarely, sutures left behind inside the airway branches can cause coughing. A cough can be triggered by dryness from mouth breathing or recurrent aspiration of food intro the windpipe in people with swallowing difficulties .

Cough may also be caused by conditions affecting the lung tissue such as bronchiectasis , cystic fibrosis , interstitial lung diseases andsarcoidosis . Coughing can also be triggered by benign or malignant lung tumors or mediastinal masses. Through irritation of the nerve, diseases of the external auditory canal (wax, for example) can also cause cough. Cardiovascular diseases associated with cough are heart failure, pulmonary infarction and aortic aneurysm.

Coughing may also be used for social reasons, such as the coughing before giving a speech. Cough may also be psychogenic, which is different from habit coughing and tic coughing. [3] Coughing may occur in tic disorders such as Tourette’s syndrome , although it should be distinguished from throat-clearing in this disorder.

Given its irritant nature to mammal tissues, capsaicin is widely used to determine the cough threshold and as a tussive stimulant in clinical research of cough suppressants. Capsaicin is what makes chilli peppers spicy, and might explain why workers in factories with these vegetables can develop a cough.

IV. COMPLICATIONS

The complications of coughing can be classified as either acute or chronic . Acute complications include cough syncope ( fainting spells due to decreased blood flow to the brain when coughs are prolonged and forceful), insomnia , cough-induced vomiting , rupture of blebscausing spontaneous pneumothorax (although this still remains to be proven), subconjunctival hemorrhage or " red eye ," coughingdefecation and in women with a prolapsed uterus , cough urination . Chronic complications are common and include abdominal or pelvichernias , fatigue fractures of lower ribs and costochondritis .

V. TREATMENT

Coughs can be treated with cough medicines . Dry coughs are treated with cough suppressants (antitussives) that suppress the body’s urge to cough, while productive coughs (coughs that produce phlegm ) are treated with expectorants that loosen mucus from the respiratory tract . Centrally acting cough suppressants, such as codeine and dextromethorphan reduce the urge to cough by inhibiting the response of the sensory endings by depolarization , or a dulling, of the vagus nerve , the nerve leading from the brain stem and serving the chest area.

Research has demonstrated that gargling with a mixture of warm water and salt washes away the layer of mucus on the throat containing bacteria and proteins that cause inflammation, according to the American Academy of Otolaryngology.